Inshot burners

bimetallic flame-proving system

Heat from the pilot light warps a bimetal switch closing the contacts to the main burner solenoid. When the pilot light goes out, the switch changes to the cold position and shuts off the main gas burner.

servo pressure regulator

flame rectification flame-proving system

The flame is located between two electrodes of different sizes. The electrodes are fed with an alternating current from the furnace's electronic module or controller. Current will flow in one direction greater than the other because of the different size electrodes. The flame actually acts as a switch. When the flame is present, the switch is closed and will conduct electricity.

induced draft system

intermittent pilot gas valve system

the pilot will be lit every time there is a call for heat by the thermostat. Once the pilot is lit and proved, usually by flame rectification, the pilot will light the main burner. Once the call for heat ends, the pilot will be extinguished and will not be re-lit until the next call for heat. In other words, there is automatic and independent control of the gas flow for both the pilot and main burner

dew point temperature (DPT)

two-stage gas furnace

uses a two-stage gas valve and a two-speed combustion blower motor with two pressure switches to prove the draft; controls the temperature in the conditioned space much closer to the set point of the thermostat. Because of this, room temperature swings are smaller and comfort levels are increased.

modulating furnace

uses a modulating gas valve instead of a staged gas valve. They also come with a variable speed warm air blower to vary the speed and amount of warm air. Two-stage combustion blower motors are usually standard. An advanced intelligent integrated furnace controller (IFC) monitors and controls the furnace operations to vary the heating input and warm airflow.

positive pressure venting system

pre-purge

allows the combustion blower motor to run for a certain time period to clear the heat exchanger of any unwanted flue gases, household fumes, or dust that may have accumulated during the last heating cycle.

direct-vented furnace

difference between a single rod and dual rod system

Flame rectification systems can be classified as either single rod (local sensing) or dual rod (remote sensing). Single-rod systems consist of an igniter and a sensor all in one rod. Dual rod systems use a separate igniter and flame sensing rod.

four types of gas burners

difference between a hard and soft lockout

Hard lockout is a time period built into the module that allows for a certain time to light or re-light the pilot or main burner. If this time period is exceeded, the module will go into a hard lockout or shutdown. Soft lockout is a time period built into the module that allows for a certain time to light or re-light the pilot or main burner. If this time period is exceeded, the module will go into a semi-shutdown for a certain time period, but will eventually keep trying to re-light the system.

non-direct vented furnace

hot-surface ignition system

draft diverter

induces air from the room while the furnace is operating to cool and dilute the flue gases. Should there be a downdraft from the flue, it allows air to spill out into the room rather than impinging on the burner flame.

Upon testing a motor run winding for continuity, the technician records 3 ohms. The winding resistance should read 8 ohms. The technician concludes that ___________.

The temperature rise of a particular furnace states that it should be between 35 and 65 degrees F. The furnace is operating at 20 degrees F temperature rise with the proper gas pressure at the manifold. What could be done to solve this problem?